Design, analysis and application of stator-permanent-magnet motors with magnetic differential

Abstract

The energy crisis and environmental concerns have prompted the recognition of the necessity to transition from internal combustion engine vehicles (ICEVs) to electric vehicles (EVs). However, despite the advantages of electric vehicles, such as reduced carbon dioxide emissions and environmental friendliness, limitations in batteries and charging stations have hindered their convenience in terms of range capability compared with ICEVs. Therefore, improving the range capability of electric vehicles through advancements in propulsion system design is a topic worth exploring. As crucial components of the propulsion system, electric motors and transmission structures has garnered significant attention. Permanent magnet (PM) motors are popular due to their high efficiency, power density, and torque density. Additionally, based on the principle of magnetic field modulation, stator-PM motors can be tailored to meet various requirements with their flexibility in motor structure. Consequently, a novel motor with the application of magnetic differential (MagD), which integrates the functions of motor and differential together, has been proposed. The MagD motor offers merits such as high integration, simplification of the electric vehicle powertrain, reduction in the onboard weight, and improved transmission efficiency, ultimately aiming to increase the range of electric vehicles. This thesis firstly presents an overview of the development of the differential mechanisms in EVs focusing on their operation principles and the characteristics. After reviewing the current differential mechanisms as well as related research, a new possible differential, MagD, which unites the traction motor and differential together, are thoroughly investigated in this thesis. Three typical types of motors with the axial-flux (AF) dual-rotor (DR) stator-PM feature with the application of the MagD are studied to show the feasibility of the MagD motors, with emphasis on their electromagnetic performances. Then, due to the better rotor decoupling feature, the flux reversal PM (FRPM) MagD motor is furtherly studied. A prototype of the proposed FRPM MagD motor has been built to verify the theoretical analysis. Both finite element analysis (FEA) and experimental results are provided to validate the idea of the FRPM MagD motor. Furthermore, a radial-flux (RF) DR FRPM motor is also examined, highlighting the balance of the torques on the two rotors by optimizing the structural design. Finally, given the risk of the demagnetization, the significant attraction force even when no-load, and the high cost of the PM materials, an alternative solution is proposed, which replaced the PM materials by the DC excitation. The toroidal DC winding installation was proposed to enhance the torque density and efficiency, and a comprehensively comparison between the FRPM MagD motor and the DC one has been presented in this thesis.